Energy required to move fluids from one location to another by a conduit or pipe is dependent upon the viscosity of the fluid, diameter of the pipe, and many other factors. The pressure in the conduit immediately adjacent the discharge side of a pump is greater than the pressure further along the conduit downstream of the pump. Part of this difference in pressure, or pressure drop, is due to friction loss or drag and is more pronounced the faster the fluid flows.
Many methods have been known for reducing the friction loss or drag of fluids flowing through conduits. Primarily, such methods for hydrocarbon transport include the use of additives known as drag reducers as presented by materials such as polyisobutylene or higher molecular weight polyalphaolefins. Generally such additives are added to the flowing hydrocarbon or as an 8-12 weight percent active solution of the additive which dissolves in the flowing hydrocarbon fluid.
Most friction loss control additives work well so long as they are not subjected to excessive shear once dissolved in the flowing hydrocarbon. Mere passage of the liquid through a conduit when the fluid is in the early stages of turbulent flow is not particularly detrimental. However, in most pipeline applications, with increasing turbulent flow and especially when passing through a pump utilized to move the hydrocarbon fluid, these polymeric drag reducers are known to shear and severely degrade the flow improving additives.
These flow improving additives are normally non-crystalline, hydrocarbon soluble polymers which have a molecular weight above about 1.times.10.sup.6 and which are capable of reducing turbulent flow in such flowing hydrocarbons. Such materials are very tacky, tend to reagglomerate, and normally are handled as partially dissolved, low active, extremely viscous solutions. However, the cost of moving the dissolved solution over great distances to where drag reduction injection is needed is expensive and requires specialized transportation and pumping equipment.
Although it is possible to ship such polymers in bulk and convert such polymers to master batch partially dissolved solutions at the injection site, typically using part of the pipeline contents as solvent, in practical terms the number of separate dissolving machines or storage vessels and cost of dissolving bulk polymers becomes prohibitive. Economically, it is strongly preferred to employ a higher active, formulated product ready for injection, rather than to be involved with bulk polymer dissolving operations.
Grinding such polymer products into fine resins prior to transportation to form particles which dissolve more readily is prohibited by the extreme reagglomeration tendencies of such polymers. If the polymers are even partially dissolved to prevent such reagglomeration, milling provides high risk of shear degradation of the polymer. In addition, finely divided polymer particles increase the probability of polymer oxidation, which lowers the molecular weight and thus the drag reduction efficiency of the polymer.
It would therefore be of great benefit to provide a method whereby such polymers could be placed into a form which is easily handled, protected from oxidation inexpensively shipped and yet dissolve readily at the point of injection such that drag reduction can be obtained. In addition, controlling dissolution at a point in the pipeline downstream of the injection point would be greatly desirable.
I have now discovered that high molecular weight, non-crystalline polymers can be placed in such a form by micro encapsulation techniques which are known to those skilled in the art, transported to the point of use as a free-flowing particulate material, and then placed into contact with the flowing hydrocarbon fluid by mechanical shearing, dissolving, leaching or melting the encapsulating material or a combination of these. In addition, the encapsulating material can be utilized to produce particles of varying particle size, wall thicknesses or a combination of these, such that the flow improving properties of the encapsulated polymer material can be realized for very rapid release or for controlled release, by temperature, shear or both temperature and shear, as the hydrocarbon fluid flows through conduits.
The prior art is aware of methods for preparing microcapsules by polymerizing urea and formaldehyde in the presence of various materials to form a wall membrane of a urea formaldehyde resin around droplets of hydrophobic oily liquids as proposed in U.S. Pat. No. 4,356,109. In addition, U.S. Pat. No. 4,001,140 discloses a process for performing encapsulations by an in-situ polymerization reaction to yield capsule wall material. The polymerization reacts urea and formaldehyde in an aqueous vehicle and allows manufacture of microcapsules at high concentrations.
U.S. Pat. No. 3,928,230 relates to the microencapsulation of fluids and solids, utilizing capsules having walls of epoxy and similar polymers. However, such encapsulating wall materials would be difficult to use in the present invention since the present invention depends upon the capsule shearing, capsule solubility, or capsules having a sufficiently low melting temperature such that the contents can be placed into contact with flowing hydrocarbons. U.S. Pat. No. 4,221,710 discloses that in the film art, microcapsules can be prepared by polymerizing urea and formaldehyde in the presence of arabic gum to form a urea formaldehyde resin wall around a previously dispersed hydrophobic oily solution. The method is used to provide pressure sensitive recording sheets.